1. Field of the Invention
The present invention relates to seals for solid oxide fuel cells, and specifically to seals having increased failure resistance over conventional seals.
2. Technical Background
Solid oxide fuel cells (SOFC) have been the subject of considerable research in recent years. Solid oxide fuel cells convert the chemical energy of a fuel, such as hydrogen, into electricity via electro-chemical oxidation of the fuel at temperatures, for example, of about 700 to about 1000° C., and subsequent reaction of the oxidized fuel with oxygen ions formed at the cathode by reduction of molecular oxygen.
A typical SOFC comprises a negatively-charged ion-conducting electrolyte layer sandwiched between a cathode layer and an anode layer. In a conventional design, multiple individual fuel cells are arranged in a stack such that gas-tight seals are needed along the edges of each cell and between the fuel cell stack and associated gas manifolds. The durability of such seals is often limited due to the high temperatures and the reducing and oxidizing gases present during fuel cell operation. In a fuel cell operating environment, conventional sealants, such as cements, do not typically provide the durability requisite for long-term operation of a SOFC. Seals can also be formed from other materials, such as high temperature glass frits.
Solid oxide fuel cells can undergo large thermal cycling and large thermal gradients, inducing thermal stresses in the fuel cell stack components. Seal failure can occur as a result of deterioration of seal materials and/or fracture or delamination of a seal material. Such failure can be detrimental, resulting in the loss of electrical current, damage to fuel cell components, and the escape and/or combination of fuel and reactant gases.
Thus, there is a need to address seal failure and other shortcomings associated with conventional seals and methods for sealing solid oxide fuel cells. These needs and other needs are satisfied by the seals and methods of the present invention.